Obese patients are at increased risk for kidney disease due to circulation of pro-inflammatory mediators and underlying renal metabolic and hemodynamic disturbances, including glomerular hyperfiltration. These patients also have unfavorable lithogenic urinary metabolic profiles, such as low urinary pH, hypocitrituria, hyperuricosuria, that predispose them to kidney stone disease. Gastric operations, in particular Roux-en-Y-gastric bypass (RYGB), are increasing as an interventional strategy to facilitate weight loss in this population. Despite the theoretical renal advantages gained during weight loss for glycemic and hypertension control, up to 75% of RYGB patients will develop sustained hyperoxaluria post-operatively, and a subset will develop kidney stones, nephrocalcinosis, impaired renal function, or even renal failure due to oxalate nephropathy. Currently, the mechanisms behind these adverse renal events are unknown. Preliminary data from an obese rat model of RYGB surgery indicates that gastric bypass causes more glomerular injury, interstitial macrophage migration, increased osteopontin production than sham surgery or pair-fed obese controls. Therefore, we hypothesize that obesity is a low-grade inflammatory process that amplifies renal host responses to RYGB-associated hyperoxaluria. In this setting, glomerular, interstitial, and papillary cells are chronically exposed to high amounts of oxalate and/or calcium oxalate crystals, leading to the production of reactive oxygen species, oxidative stress, renal injury, and inflammation. The objective of this application is to provide a training environment for the principal investigator to examine the role of RYGB-associated hyperoxaluria in the development of renal injury and nephrolithiasis, with special focus on renal histology, transport physiology, tissue proteomics, and genomics.
Our specific aims are: 1) To further characterize renal effects of RYGB surgery in a diet-induced obese rodent model versus controls by comparing metabolic profiles, pro-inflammatory mediators, histology, protein expression, and pathway-focused gene expression profiles;2) To further our understanding of RYGB induced hyperoxaluria by investigating segmental differences in intestinal oxalate handling and the effect of Oxalobacter colonization on urinary oxalate levels;3) To compare protein and gene expression profiles from renal papillary tips of human RYGB stone formers with and without Randall's plaque deposition. Understanding the mechanisms of hyperoxaluria following RYGB will provide insights into the pathogenesis of oxalate nephrolithiasis associated with obesity. My K08 program is structured to allow me to further explore relevant rodent models of obesity, to validate preliminary hypothesis generated by a recent minority supplement award, to enhance my understanding of oxalate transport within the gut and kidney, and then, most importantly, translate these efforts into mechanisms of disease within human renal tissue.
Morbidly obese patients who undergo Roux en Y gastric bypass (RYGB) may develop sustained post-operative hyperoxaluria that leads to kidney stones, impaired renal function with calcium oxalate deposition within kidney collecting ducts associated with inflammation and fibrosis, or even renal failure due to oxalate nephropathy. The objective of this application is the establishment of a training environment for the candidate to develop an animal model that explores gut and renal mechanisms of RYGB-associated hyperoxaluria in the development of renal injury and nephrolithiasis, with special focus on renal histology, transport physiology, tissue proteomics, and genomics. As a boarded urologic surgeon with a strong track record of publications in urologic stone disease, the candidate is professionally trained to develop a surgical model of stone disease and renal metabolism, and his K08 program is structured to allow him to further explore relevant rat models of obesity, to validate preliminary hypothesis generated by a recent minority supplement award, to enhance his understanding of oxalate transport within the gut and kidney, and to translate these efforts into mechanisms of disease within human renal tissue.
